On 04/24/2013 06:35 PM, Steven D'Aprano wrote:
Objects are supposed to return NotImplemented from special dunder methods
like __add__, __lt__, etc. to say "I don't know how to implement this
method for the given argument". Python will then try calling the other
object's special method. If both objects return NotImplemented, Python
falls back on whatever default behaviour is appropriate.
So, knowing nothing of your application, I fear that this is an abuse of
NotImplemented's semantics. If a rule returns NotImplemented, I would
expect your application to fall back on a different rule. If that's not
the case, you're using it in a non-standard way that will cause confusion
for those with expectations of what NotImplemented means.
Why would you assume some random application is going to deal with NotImplemented the same way the python interpreter
does? And even the interpreter isn't consistent -- sometimes it will return false (__eq__) and sometimes it will raise
an Exception (__add__).
I hardly think it an abuse of NotImplemented to signal something is not implemented when NotImplemented means, um, not
implemented.
possibly-not-implemented-ly yours,
--
~Ethan~
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